The present invention relates generally to airborne monitoring systems, and more particularly to a novel and improved unpowered airborne data collection system and method especially suitable for observing tropical cyclones and other meteorological, environmental, radiological and surveillance phenomena in the lower atmospheric boundary layer.
Tropical cyclones are one of nature's most devastating phenomena. Approximately 100 tropical cyclones, with hurricane force winds, occur each year causing an average of 20,000 deaths and six to seven billion dollars in economic loss. For instance, winds associated with Hurricane Andrew in 1993 resulted in damage to areas of southern Florida and Louisiana of over twenty billion dollars. Tropical cyclones occur over warm ocean waters in the tropics, and are called hurricanes if they form in the West Indies, and typhoons if they form in the Pacific Ocean. In the case of a hurricane, the center or eye travels from 10 to 30 miles per hour slowly westward at first, then picks up speed and turns toward the pole, and finally eastward as it reaches more temperate latitudes.
Tropical cyclones are characterized by a wind pattern which spirals inward with a negative pressure gradient (rotating counterclockwise in the Northern Hemisphere) reaching wind speeds of 110 to 200 mph immediately outside a relatively calm eye region about 20 miles across. The wind speed typically decreases to under 10 mph on transition through the wall of the eye. Intense convective activity and precipitation occur in spiral rain bands within 60 miles of the eye and, on land fall, produce tidal waves and severe thunderstorms which frequently spawn tornados.
Accurate continuous monitoring of tropical cyclone eye location, speed and direction of travel, central barometric pressure, and wind speed at the eye wall are critical for predicting storm intensity prior to landfall. These observations have been carried out in situ by manned hurricane-tracking aircraft, and remotely by free-floating balloons and satellite systems. While aircraft can provide essential atmospheric data, they entail some risk to its crew and are normally limited to altitudes at or above the boundary layer of the sea-air interface (approximately 1000 meters). In addition, they have limited on-station time, and at $20,000 to $30,000 per sortie, are prohibitively too expensive for many tropical cyclone-intense countries of the world.
Satellites provide excellent tracking data but rely on pattern recognition techniques that are subject to large random and systematic errors. Even though ground-truth measurements may significantly enhance the information obtained from the satellite imagery they cannot provide reliable local atmospheric conditions in the atmospheric boundary layer.
Free-floating balloons, also referred to as hurricane beacons, are designed to be released in the eye of a tropical cyclone, float with the eye at a predetermined level, and transmit observed data by radio signals. Due to extreme variations and wind conditions, they are incapable of maneuvering themselves from the periphery of the tropical cyclone into the eye or of maintaining a constant altitude in the lower atmospheric boundary layer.
If meteorological measurements from the eye of a tropical cyclone at near-surface altitudes of 800 to 1000 feet were possible, the intensity could be forecasted with a high confidence level thereby avoiding unnecessary evacuations for public safety and the production losses that may follow. However, such near-surface weather data within the core of tropical cyclones has not been readily available to meteorologists, the most important data being tropical cyclone eye location, speed and direction of travel, central barometric pressure, and wind speeds at the eye wall. If only the vicinity around the eye of a tropical cyclone were not such a violent region, a variety of robust surface and heavier-than-air vehicles could directly penetrate the eye of the storm at a low altitude, travel with the storm and broadcast the data.
Heretofore, prior art systems have been incapable of providing such a low-level track for continuously observing the intensity of tropical cyclones in real time without imposing severe limits on the system's endurance. Consequently, there is a need for an inexpensive in situ sensor platform which can sustain itself at low relative velocities and lower stresses by riding with the local near-surface flow pattern of a tropical cyclone.